1. Field of the Invention
The invention relates to an LED device manufacturing method and LED device. Particularly, the invention relates to a method for manufacturing an LED device and an LED device that emits light of a given color tone by additive color mixture. The additive color mixture includes mixing light emitted directly from an LED chip and light that has been obtained by wavelength conversion of some of the light emitted from the LED chip by use of a wavelength conversion material, e.g., fluorescent material.
2. Description of the Related Art
An LED chip can emit light having a steep spectrum distribution. In order to achieve an LED device for emitting white light using an LED chip as a light source, additive color mixture has been adopted. The additive color mixture is achieved by mixing the light emitted from the LED chip with light obtained by wavelength conversion of the light emitted from the LED chip by means of a wavelength conversion material such as a fluorescent material that is excited by the light emitted from the LED chip.
When an LED chip that emits blue light is used, for example, a fluorescent material that is excited by the blue light and converts the blue color into yellow or a complementary color of blue is used. Thus, white light can be obtained by additive color mixture of the blue light emitted from the LED chip and the yellow light obtained by wavelength conversion by means of the above fluorescent material.
Alternatively, two fluorescent materials that are excited by the blue light and convert the blue light into green light and red light, respectively, may be used. In this case, white light can also be obtained by additive color mixture of the blue light emitted from the LED chip with the green light and the red light obtained by wavelength conversion by means of the above two fluorescent materials.
When an LED chip that emits ultraviolet light rays is employed, three fluorescent materials that are excited by the ultraviolet rays and convert the ultraviolet rays into blue light, green light, and red light, respectively, are used. In this case, white light can also be obtained by additive color mixture of the blue light, the green light, and the red light obtained by wavelength conversion by means of the above three fluorescent materials.
Moreover, light of various color tones other than white light can be obtained by appropriately combining a color of light emitted from an LED chip with a fluorescent material serving as a wavelength conversion member.
The aforementioned LED device that emits light of a different color tone from that of light emitted from its light source (by exciting a fluorescent material with the light emitted from the light source to cause wavelength conversion) may have a structure as shown in FIG. 1, for example. This type of LED device has a pair of conductor patterns 50 and 51 formed on surfaces of an insulating substrate so as to serve as a double-face through-hole substrate 52. The substrate 52 has a cone-shaped concave portion 53 formed therein. One conductive pattern 50 forms a bottom 54 of the concave portion 53 and serves as an electrode portion provided on the rear surface of the insulating substrate. The other conductor pattern 51 formed on the top surface of the insulating substrate extends to the rear surface through a through hole 55 and forms another electrode portion provided on the rear surface.
An LED chip 56 is mounted on the bottom 54 of the concave portion 53, or on a part of the conductor pattern 50, via a conductive adhesive. A lower electrode of the LED chip 56 is electrically connected to the conductor pattern 50. An upper electrode of the LED chip 56 is electrically connected to the conductor pattern 51 via a bonding wire 57.
A first resin 58 into which a fluorescent material for wavelength conversion is added is filled in the concave portion 53 in which the LED chip 56 has been mounted so as to embed and encapsulate the LED chip 56. Then, a resin encapsulation including a second resin 59 that contains a transparent epoxy resin as a major component is formed on the double-face through-hole substrate 52 including the concave portion 53. A hemispherical condenser 60 is also formed above the center of the double-face through-hole substrate 52 and can be integrated with the encapsulation of the second resin 59 (see Japanese Patent Laid-Open Publication No. 2002-324917, for example).
As shown in FIG. 2, another LED device is known that will be described as a conventional technique and is disclosed in Japanese Patent Laid-Open Publication No. 2003-258310. This LED device has a pair of conductor patterns 70 and 71 formed on an insulating substrate in such a manner that each conductor pattern extends from a top surface of the insulating substrate to a rear surface via a side face, thereby forming a wiring substrate 72. An LED chip 73 is mounted on one conductor pattern 70 via a silver adhesive paste. A pair of electrodes that are formed on the top of the LED chip 73 are connected to the conductor patterns 70 and 71 via bonding wires 74 and 75, respectively, so as to electrically connect the electrodes to the conductor patterns 70 and 71. The LED chip 73 and the bonding wires 74 and 75 are encapsulated with an encapsulating resin 77 containing a transparent resin formed of an epoxy resin, for example, and a fluorescent material 76.
In the conventional LED device configured like that disclosed in Japanese Patent Laid-Open Publication No. 2002-324917, the LED chip mounted in the concave portion is embedded and encapsulated by filling the concave portion with a first resin into which a material for wavelength conversion is added. Thus, a light-emitting surface of the LED chip is in direct contact with the first resin. Therefore, a color tone of light that is emitted from the LED chip and that is transmitted through the first resin is directly changed by variation of a thickness of the first resin on the light-emitting surface of the LED chip. Accordingly, control of the amount of the first resin in the concave portion is important in order to keep a color tone of light emitted from the LED uniform and highly reproducible.
One of the typical requirements of an LED device is reduction of its size. Thus, making the dimensions of the concave portion in which the LED chip is mounted as small as possible is often desired. In this case, however, the amount of the first resin in the concave portion is very small and therefore it is difficult to control the amount of the first resin and to reproduce that amount.
When the first resin is supplied into the concave portion, a discharging device for discharging liquid of a constant amount, such as a dispenser, is generally used to supply a constant amount of the first resin discharged from a nozzle of the device into the concave portion. However, in the LED chip mounted at the substantial center portion of the concave portion, the bonding wire extends above an opening of the concave portion and is arranged to cross the opening of the concave portion. Thus, the bonding wire obstructs the resin discharged from the nozzle of the device, making injection of the resin unstable. Therefore, the amount and characteristics of the injected resin are unstable.
On the other hand, in the conventional LED device disclosed in Japanese Patent Laid-Open Publication No. 2003-258310, when the encapsulating resin that includes the transparent resin and the fluorescent material is heated to be hardened, the fluorescent material which has a larger specific gravity than that of the transparent resin settles down due to a difference in specific gravity between the fluorescent material and the transparent resin. Thus, it is difficult to disperse the fluorescent material uniformly in the encapsulating resin. Moreover, it is also difficult to consistently achieve a mixing ratio of the transparent resin and the fluorescent material in the encapsulating resin with high precision and high reproducibility. Accordingly, uniformity of light emitted from the LED to the outside (to the air) is impaired and a tone difference between products can occur.
In addition, when a convex condenser is provided on the light-emitting surface of the above-described LED chip and on an optical axis of the LED chip, light emitted from the LED chip is diffused by the fluorescent material contained in the encapsulating resin. Thus, a required focusing effect of the lens, or a required light distribution property, can not be obtained.
In a conventional technique, the fluorescent resin is directly injected into a first cup. However, a bonding wire extends above the opening of the first cup in which the LED chip is mounted approximately at the center to cross the opening of the first cup. Thus, injection of the fluorescent resin discharged from the nozzle of the device into the first cup is not assured, because the bonding wire obstructs that injection. For this reason, the injection amount may not be stable.